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Australian scientists are warning that people may be exposed to potentially deadly bacteria if they touch their mouths or eat without washing their hands after coming into contact with surfaces contaminated with gull poop

Adult silver gull (Chroicocephalus novaehollandiae) in Victoria, Australia. The silver gull is the most common gull species in Australia.(Credit: Fir0002 / GFDL 1.2)

Fir0002 via a Creative Commons license

Australian gulls have been discovered carrying antibiotic-resistant “superbugs” that could cause serious infections in people, pets and livestock, according to an international team of scientists led by researchers at Murdoch University in Perth.

According to their findings, more than one in five silver gulls, Chroicocephalus novaehollandiae, were estimated to carry pathogenic E. coli bacteria that could cause urinary tract infections, pneumonia, sepsis (a bacterial infection of the blood), and rarely, meningitis (an inflammation of the tissues surrounding the brain).

“These are common pathogenic bacteria we see in humans in Australia. These bacteria colonise the human gut and then cause disease when they get an opportunity,” said microbiologist Sam Abraham, a lecturer in veterinary and medical infectious disease at Murdoch University and co-author of the study.

Escherichia coli, abbreviated as E. coli, are common bacteria found in the environment, in foods, and in the guts of people and animals. Although they are usually harmless members of a normal gut microbial community, E. coli is a large and diverse group of bacteria, and some strains are pathogenic. Thanks to improper use of antibiotics, E. coli are developing antibiotic resistances, which they then share with “naïve” E. coli as well as with other types of bacteria, effectively transforming once-treatable microbes into deadly “superbugs”.

“What we found, which we didn’t expect to find, was the high levels of resistant E. coli that the seagulls were carrying -- that was quite unusual,” said co-author, Mark O’Dea, a senior lecturer in veterinary virology at Murdoch University.

Antibiotic-resistant bacteria are common in hospitals, convalescent centers and nursing homes, but this is the first time they’ve been detected in Australian wildlife.

These antibiotic-resistant superbugs are human in origin: the gulls initially became infected after coming into contact with human feces, probably by consuming food contaminated by human sewage or by discarded diapers. Australians use 3.75 million disposable diapers every day, which amount to a significant proportion of the household waste entering landfills.

Silver gulls “may then be subsequently spreading these resistant bacteria over vast distances,” Dr. Abraham said in email, noting that the gulls can fly 1,600km (1000 miles) or more away from their nests.

The gulls may spread these bacteria to other bird species along the way, which could then travel to farming areas in Australia where, it is feared they may pass these pathogenic bacteria to livestock. According to the Australian government, effective policies have been implemented to prevent and manage antimicrobial resistance in food producing animals (more here), making its livestock amongst the “cleanest” in the world. Although it’s a longshot, it’s feared that the gulls may possibly give these antibiotic-resistant bacteria back to people.

Adult silver gull (Chroicocephalus novaehollandiae) in flight. You may be looking at this gull, but it’s looking at your lunch.(Credit: Peakpx / CC0)

Peakpx / Public domain

What motivated Dr. Abraham and his collaborators to examine the microbes that these gulls carry?

“We saw few small studies around the world in urban birds and wanted to know what was happening in gulls in Australia,” Dr. Abraham replied in email.

Silver gulls were the obvious choice: they are the most common gull species in Australia and they are especially common on beaches and coastal areas where large groups of people tend to congregate.

Dr. Abraham and his collaborators chose sampling locations that were widely dispersed around the perimeter of the Australian continent, with sites separated by up to 3500 km (2200 miles). Between 2015 and 2017, the researchers collected 562 poop samples from silver gulls from populated beaches across the eastern (n = 384), western (n = 144) and southern (n = 34) states of Australia. They tested each gull’s fecal bacteria for resistances against 12 antimicrobials, and found more than 20% of the samples contained antibiotic-resistant E. coli bacterial isolates.

“What we found was, regardless of the state, the gull population in Australia are carriers of superbugs, or antimicrobial resistant bacteria, that cause infection in humans,” Dr. Abraham said. “These are the ones that are resistant to drugs of importance to human health, that is where our initial concerns are.”

The E. coli isolates were resistant to cephalosporins (22%), which are broad spectrum antibiotics that are similar to penicillin, and fluoroquinolones (24%), which are commonly used to treat respiratory and urinary tract infections (Figure 1).

Astonishingly, several E. coli strains were so virulent that they could withstand even last-resort antimicrobial drugs.

One resistant E. coli strain carried by a gull in Victoria was discovered to be resistant to carbapenems, which are a class of highly effective antibiotic agents used to treat antibiotic resistant bacterial infections when other anti-bacterial drugs fail. (Carbapenems are typically unaffected by emerging antibiotic resistance, even to other commonly prescribed beta-lactam antibiotics; ref.)

Even more concerning, the researchers discovered another gull at Cottesloe Beach in Western Australia carrying an E. coli strain that was resistance to colistin, which is an antibiotic of last resort in the fight against multidrug-resistant bacterial infections. This is the first time that this antibiotic resistance has been detected in any wild animal in Australia, according to the report, although it has recently been detected in birds in South America (ref) and in Asia (ref).

Where did these antibiotic-resistant superbugs originally come from? Whole genome sequencing revealed that the carbapenem resistant E. coli strain was originally identified in Turkey in 2018 (ref), but it has since has been established as one of the internationally emerging ‘high-risk’ clones (ref).

Household waste must be disposed of properly to protect people, pets and wildlife

It’s no secret that poor management of medical, biological and food waste is likely the source of antibiotic resistant bacteria and other pathogenic microbes in wild birds, especially gulls, which are opportunistic foragers.

This study raises the concern that gulls “could be acquiring this pathogen through their opportunistic feeding habits where they scavenge from leftover human waste,” Dr. O’Dea said.

“We do have a problem where we have a high proportion of gulls that scavenge where food waste gets mixed in with faeces, like nappies and incontinence pads from nursing homes,” Dr. Abraham said.

Are these superbugs making the gulls ill?

“No. The gulls are perfectly fine,” Dr. Abraham said in email. “They act as ecological sponges that pick up drug resistant bacteria and spread them around.”

Silver gulls are probably not the only wild birds carrying antibiotic-resistant E. coli: for example, the Australian white ibis, Threskiornis molucca, commonly forage in urban trash bins -- a habit that has earned them the patronizing nickname “bin chickens” -- and a variety of wild migratory duck species settle on human and livestock sewage settling ponds to feed and rest.

Australian white ibis (Threskiornis molucca), in Perth, Australia. Because these birds often forage in urban rubbish bins, they are colloquially referred to as “bin chickens”.(Credit: JJ Harrison / CC BY-SA 3.0)

JJ Harrison via a Creative commons license

Have the scientists found antibiotic-resistant bacteria these, or in any other, wild birds?

“We have a current study running in other wild birds but the results are not available yet,” Dr. Abraham replied in email.

Dr. Abraham and his collaborators hope this study will cause the Australian government to change how it manages waste created by farm animals, and especially by people, by developing methods for preventing scavenging birds’ access to this waste.

“I think that it is a wake-up call for all government and various agencies, like water treatment and big councils that manage waste, to properly work collaboratively to tackle this issue,” Dr. Abraham said.

“It could be as simple as putting nets on open sewerage areas, scaring the birds off from getting into food waste and processing soiled nappies and incontinence pads separately,” Dr. Abraham added.

Of course, people have a responsibility use some common sense and practice good hygiene by washing their hands before eating, and after touching surfaces, such as outdoor picnic tables, that potentially have been contaminated by gull poop.

Although Dr. Abraham advocates the use of hand sanitizers, it’s important to point out that antibiotic resistant bacteria are also becoming resistant to alcohol-based hand sanitizers, as reported by a team of scientists from the University of Melbourne in the early 2000s (ref).

“We’re only scratching the surface at the moment; it’s the tip of the iceberg”, Dr. Abraham added.